class Queue {
    constructor() {
        this.items = []
    }
    enQueue(item) {
        this.items.push(item)
    }
    deQueue() {
        return this.items.shift()
    }
    front() {
        return this.items[0]
    }
    isEmpty() {
        return this.items.length == 0
    }
    size() {
        return this.items.length
    }
    toString() {
        var resultStr = ''
        for (let i = 0; i < this.items.length; i++) {
            resultStr += this.items[i] + ''
        }
        return resultStr
    }
}